<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        * {
            margin: 0;
        }
        .center {
            width: 1000px;
            margin: 0 auto;
        }
        .card {
            height: 300px;
            background-color: pink;
            border: 5px solid red;
        }
        span {
            /*行内元素上下间距均无效*/
            background-color: rgba(0,0,255,0.3);
            margin: 50px 25px;
            padding: 50px 25px;
        }
    </style>
</head>
<body>
    <div class="main">
        <div class="center">
            <div class="card"></div>
        </div>
    </div>
    <hr>
    <span>123456789</span>
    <span>123456789</span>
    <span>123456789</span>
    <div class="main">
        <div class="center">
            <div class="card"></div>
        </div>
    </div>
    <hr>
</body>
</html>